The topic we are going to discuss today will fit into visual analytics and data visualization – 101. Though on the surface this is really simple, over the years I have seen many young and sometimes seasoned analysts make this mistake. Hence I feel it is apt for us to discussion the topic about appropriate usage of graphical and visual tools to communicate information and analytical storytelling. To understand this better let us take a simple example and ask the following question: which is a better choice of chart to present information –
Pie Chart or Bar Chart?
To answer this question, let us consider the population of six most populated cities in the world (in alphabetical order)
Here is a task for you – arrange these cities in the descending order of population – take a guess. Please don’t read further till you complete this task. Now, to help you out let me display the actual population of these cities in form of a pie chart, as displayed below.
Before going further, use the above pie chart to rearrange your guess for the cities in descending order of population. Just take a pause and think, how useful is a pie chart to compare the magnitude of the data?
Now, let us plot the same information using a bar chart. You may want to revisit your list and use the following bar chart to rearrange the cities in descending order of population.
Is the bar chart more helpful to rearrange the cities in descending order of population than the pie chart? I think the answer is yes and is fairly obvious. These are the conclusions one could draw:
- Shanghai is definitely on top
- Followed by Lagos at number two
- In terms of population, Karachi and Istanbul are actual quite similar. Karachi’s population is just 0.5% more than Istanbul (statistically not much to choose).
- Mumbai (yeah that’s my city) is at number five followed by Moscow
Let me pose a few questions for all of us to discuss
- Why did the bar chart work better than the pie chart?
- What concepts one should keep in mind while presenting information/data to a larger audience?
- Is it even important to convey data in ways that are easy for the audience to understand? Why bother?
You could post your answers / ideas / thoughts / challenges / comments on the ‘Leave a Reply’ section underneath. Let’s discuss.
For further discussion, let me share an unwritten rule among analysts regarding bar charts and pie charts. For all practical purposes, the rule is to never use pie chart and if you really have to, think for a while and then use bar chart. Does this make sense?